The invention relates generally to electrodes for electroactive devices. The invention particularly relates to electrodes for organic electroactive devices.
Organic electroactive devices include organic light emitting devices and organic photovoltaic devices. Organic electroactive devices operate by injection of charges, which combine to result in radiation of energy as in a light emitting device, or by separation of charges as in a photovoltaic device. Efficient operation of electroactive devices depends, among other things, on efficient transport of charges across an interface between an electrode and an adjacent medium.
Metals having low work functions, desirably lower than 4.0 eV such as alkali and alkaline-earth metals, are often used as cathode materials to promote electron injection. Cathode materials such as calcium, lithium, and cesium, used to promote electron injection, are usually reactive metals and are sensitive to moisture and oxygen and degrade upon exposure to the environment. A hermetic seal is thus required to prevent exposure of such cathode materials to oxygen and moisture. Conventionally, devices using these metals as cathode materials are often encapsulated to prevent oxygen and moisture from reaching the active components of the device. Capping layers including less reactive metals, such as aluminum, have also been used to cover and protect layers with such cathode materials. Disadvantageously, capping layers may be prone to pin holes and defects, which allow moisture and oxygen to permeate through to the reactive cathode materials.
Accordingly, a technique is needed to address one or more of the foregoing problems in electroactive devices, such as organic electroactive devices.